Spin- and energy relaxation of hot electrons at GaAs surfaces

The mechanisms for spin relaxation in semiconductors are reviewed, and the mechanism prevalent in p-doped semiconductors, namely spin relaxation due to the electron-hole exchange interaction, or Bir-Aronov-Pikus mechanism, is presented in some depth. It is shown that the solution of Boltzmann-type kinetic equations allows one to obtain quantitative results for spin relaxation in semiconductors that go beyond the original Bir-Aronov-Pikus relaxation-rate approximation. Experimental results using surface-sensitive two-photon photoemission techniques show that the relaxation time of the electron spin polarization in p-doped GaAs at a semiconductor/metal surface is several times longer than the corresponding bulk spin-relaxation times. A theoretical explanation of these results in terms of the reduced density of holes in the band-bending region at the surface is presented.